Which pivot pin?

[Frank Niro]

Please tell me the need for the bushings. I believe in the K.I.S.S. prinipal. (Keep it simple, stupid) I use a 1/8" stainless pivot that passes through titanium liners. On each side of the blade I usually use a .0015 washer made of nylon. I tighten down the screws so that they bottom after I add a drop of non permanent locking Locktite. The blades of my folders are known to have very smooth easy movement witout any side play of course.Ones that have seen hard useage that I've had a chance to check out haven't shown any noticable wear. If the bushings are to make the pivot stronger, I suggest simply going to a larger pivot. Hey, what am I missing out on doing it this way? Frank

[David Broadwell]

Originally Posted by Bob Cannon

Ok guys, I'm learning quite a bit.

David, what is a barrel lap and how do you do it? Thanks.

Bob,

Glad you're learning! A barrel lap is a tool for truing up and adjusting the size of a hole. Some are for blind holes, others for through holes. It consists of a steel rod that is chucked in your drill press, an adjustable brass lap screwed onto the end of the rod, and an adjustment screw in the end of the lap. Some ream their pivot holes in the blades slightly undersize (I just have worn reamers!), then lap them to size after heat treating. You adjust the lap so that it will just slip through the hole. While spinning (600 to 1000 RPM is what I use) you add a bit of valve grinding compound. Making sure your drill press table is flat and perpendicular with your spindle, you run the lap up and down through your hole. When you feel less resistance, pull it out and clean the hole. Gage it for size. I use a pivot. If it's small, you turn the adjuster screw in the end a little to expand the lap, then repeat the process. With some practice you can hold very tight tolerances.

The lap works by imbedding the abrasive compound in the softer brass and cutting the harder steel. Very small adjustments of the screw yield very small size increases. The laps will give you a truer round hole if it warps slightly during heat treating. Lapping will also give you a much finer finish than reaming alone. I don't recommend that you get your hole to pivot tolerances too close. It should have some form of lubrication in there.

A quick search of MSC shows this 3/16" lap: http://www1.mscdirect.com/CGI/NNSRIT...MT4NO=55699552 I believe this is a stock photo since most of their laps use this pic. My 3/16 and 1/4 laps actually look like this one: http://www1.mscdirect.com/CGI/NNSRIT...MT4NO=55699817 Make sure they are for the size hole you are making for your pivots, they are adjustable, and for through holes.

Frank, other than size, we're on the same page. I use .015" nylon washers, but have used phosphor bronze washers. I've found that I prefer the nylon for smoothness and toughness. I found out how tough nylon was when back in about 1990 I had to change the timing gear on my 1971 Buick. With about 120000 miles on her, she slipped timing when the distributor seized. The timing chain was badly stretched and the iron crank sprocket was worn, but the nylon cam gear was in great shape. Teflon may be slicker, but how long does it last on your skillet? Nylon, helping knives work smoothly and women's legs look great since 1935!

David

[Don Robinson]

Hi, Frank. Happy new year!

A bushing serves two purposes in my knives.

1. Two similar materials rubbing together can gall ( metal rubbing together wears and attaches itself to the second part). Now notice I said "CAN". Not WILL. This is worst case scenario.

To prevent this, I use a bronze bushing inside the pivot holes in my steel blades. The dissimilar metals won't seize together. (gall), and work smoothly together with a little oil.

Another way around this is the old saying, "Hard to Hard Works". Two hardened pieces of metal won't gall. That's why some makers use a hardened stainless steel bushing.

A bushing increases the O.D. of the pivot, adding more strength and resistance to blade twisting. this is a benefit.

2. The main reason I use bushings is to tighten the liners against the ends of the bushing. That avoids the need for further adjustment and Loc-tite. there is no need to tighten or loosen the pivot screws on my folders. Simply tighten both sides all the way and the precision fitted bushing takes all the load and provides clearance for the blade to pivot at the same time.

That said, I don't use a bushing in folders that are pinned together, although that can be done. My slipjoints are made without bushings the old fashioned way.

As to whether to use bushings or not, I'd say that if you have the machinery and skills to make a precision fitted bushing, then use them. If you don't have the proper machinery and skills, then don't use bushings. The owner of the knife will probably never know the difference.

I can make a bushing to fit exactly within about 10 minutes from a bronze bar.

To make a bushing you need a good metal lathe and a precision surface grinder.

[Frank Niro]

Thanks for the replys all !!! No I don't have either a precision lathe it's cutting movements are very poor,or a surface grinder. I guess my going with the stainless pivots directly against the heat treated blades was a good thing for my use to find and go with. Frank